    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2004-152465    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2-150325
Conventionally, in a general optical disc manufacturing method, first, a disc master is manufactured. Then, a stamper is manufactured using the disc master, and disc substrates are mass-produced using the stamper. A layered structure including a reflective film, a cover layer, etc., is formed on the mass-produced disc substrates. Thus, optical discs are completed.
Here, first, the disc master is formed such that the disc master has a recess-projection pattern for forming a pit/land structure which defines information signal lines, or a recess-projection pattern for forming a groove/land structure which defines recording tracks. Then, a stamper is formed in which the recess-projection pattern is transferred in an inverted manner. Then, disc substrates having a recess-projection pattern obtained by transferring the recess-projection pattern on the stamper in an inverted manner are manufactured.
A part of a manufacturing process for manufacturing, for example, a reproduction-only optical disc having embossed pit rows defined by a pit/land structure will be described with reference to FIGS. 8 and 9.
FIG. 8(a) illustrates the manner in which a photoresist (organic resist) film formed on a master substrate made of, for example, glass, is subjected to an exposure step.
In the process of forming a disc master, a resist film 102 is formed on the master substrate, and the resist film 102 is irradiated with a laser beam L. The laser beam L is modulated on the basis of information signals to be recorded in the form of pit rows.
As shown in FIG. 8(a), portions of the resist film 102 which are subjected to the laser irradiation are formed into exposed portions 102a by optical reaction. In other words, the exposed portions 102a and unexposed portions 102b are formed as a result of the laser irradiation.
After the above-described exposure step, development is performed in a development step. As a result, as shown in FIG. 8(b), the exposed portions 102a are formed into recessed portions 110 and the unexposed portions 102b are formed into projecting portions 111. Thus, a disc master having a physical recess-projection pattern is completed. In other words, the disc master is manufactured by subjecting the organic resist to exposure with optical reaction and then developing the organic resist.
Here, in the disc master obtained by the exposure with optical reaction, boundaries between the recessed and projecting portions are generally substantially vertical. In FIGS. 8(a) and 8(b), the boundaries between the recessed and projecting portions are inclined. The boundaries having the shapes shown in the figures can be formed by the following method. That is, when the development of the disc master is performed, diffracted light (0 order light and 1st order light) is observed on a development monitor and the development is stopped in the state in which an optimum signal can be obtained instead of performing the development to the end. In this case, a higher separation performance can be obtained compared to the case in which the boundaries are closer to vertical. The development using the development monitor is commonly performed in the optical reaction method.
Next, a stamper 104 shown in FIG. 8(c) is manufactured using the above-described disc master. The stamper 104 has a recess-projection pattern obtained by transferring the recess-projection pattern on the disc master in an inverted manner. More specifically, portions corresponding to the recessed portions 110 in the disc master are formed as projecting portions 120 and portions corresponding to the projecting portions 111 in the disc master are formed as recessed portions 121.
Disc substrates are mass-produced by injection molding using the above-described stamper 104.
FIG. 9(a) shows the state in which resin (for example, polycarbonate) for forming a disc substrate 105 is injected into a mold in which the stamper 104 is placed.
FIG. 9(b) shows the state in which the resin injected into the mold is cooled.
FIG. 9(c) shows the state in which the stamper 104 is removed after the resin is cooled. Thus, as shown in the figure, the disc substrate 105 in which the recess-projection pattern on the stamper 104 is transferred in an inverted manner is obtained. In the disc substrate 105, portions corresponding to the recessed portions 121 in the stamper are formed as projecting portions (lands) 131 and portions corresponding to the projecting portions 120 in the stamper are formed as recessed portions (pits) 130.